Electrochemical Activation Behavior Of Co?OH?₂ Nanotubes By Ion-exchange Methods

As a new type of energy storage device,much attention has been paid to supercapacitors due to their advantages of fast charging/discharging rate,high energy conversion efficiency,high power density,long cycle life and safety.In the configuration of supercapacitors,active materials on the electrode are critical to their electrochemical performance.This work utilized a facile ion-exchange method to synthesize the Co?OH?₂ nonotubes with dense nanosheets on the surface.To unveil the activation mechanism of the Co?OH?₂ nonotubes during charging-discharging process,the morphology and chemical composition of the electrode were investigated before and after electrochemical test.Based on the results,a novel activation mechanism was put forward.Firstly,using cobalt chloride and urea as the main reactants,cobalt subcarbonate precursor was synthesized by a facile one-step hydrothermal method.The structure,composition and morphology of the precursor were analyzed by XRD,FTIR,SEM,TEM respectively.The results show that the as-prepared precursor is Co?CO₃?_0.5?OH?·0.11H₂O nanowire with smooth surface,the diameter of which is about 100 nm.Then,using Co?CO₃?_0.5?OH?·0.11H₂O precursor as the working electrode and 6 M KOH as electrolyte,Co?OH?₂ nonotubes were obtained by an electrochemical ion-exchange method,which was carried out in a cyclic voltammetry?CV?test.After being charged one time,XRD and FTIR characterizations demonstrate that the sample was transformed to Co?OH?₂,which implied that CO₃^2-in the precursor was exchanged with OH^-in the electrolyte.Moreover,SEM and TEM images exhibit the as-prepared Co?OH?₂ electrode possesses morphology of nonotubes with dense nanosheets on the surface.This special structure was formed by Kirkendall effect in the ion-exchange process.In order to explain the improvement of electrochemical performance during the continuous charging-discharging process,the active materials on the electrode after being charged and discharged for different time were analyzed.Depending on the XRD,FTIR,SEM,TEM,EIS characterizations,an activation mechanism of the electrode materials was discussed in details.In the process of charging-discharging,the phase of the sample was changed from Co?OH?₂ to CoOOH as well as the impedance and morphology.